The subject matter disclosed herein relates to a method used for starting an aircraft engine using a synchronous generator and a constant speed drive.
Many aircraft in service have a synchronous generator coupled to each engine through a constant speed drive (CSD). As each of the engines turn, the corresponding CSD controls an associated synchronous generator to produce a constant frequency output current that can be used in various aircraft systems. For example, a synchronous generator may be employed to provide power to the air conditioning system or other electrical systems on a commercial aircraft.
Given the power rating required to drive these electrical loads, most synchronous generators should be capable of starting the aircraft engine. The problem with this configuration is that starting an aircraft engine requires that the engine spins at varying speed ranges outside the narrow frequency band (i.e., about 400 Hz) of commonly used CSDs. As a result, in most aircraft designs, an air turbine starter is used to start the engine as there does not exist a method to vary the speed output from the CSD.